The present invention relates to apparatus for adjusting optical system of an image forming apparatus, which is mounted on the optical system for scanning and exposing the original document to light by moving first and second moving frames to which mirrors are respectively secured, and which is adapted to adjust the positional relationship between both moving frames.
Conventionally, an electrophotographic copying apparatus as an example of the image forming apparatus is provided with an optical system for illuminating an original document placed on a transparent platen, so that the reflected light from the original document is guided to the photoreceptor through a plurality of mirrors.
Generally, the first moving frame having an illumination device and the first mirror secured thereto is moved in parallel to the original document, and the second moving frame having the second and third mirrors secured thereto is moved at a speed equal to 1/2 of that of the first moving frame, such that the original document is scanned and exposed to light by the optical system. The movement of the first and second moving frames is achieved by driving a pair of wires with which the moving frames are respectively engaged.
If the positional relationship between the first and second moving frames (the parallelism and distance between both moving frames) is out of order, a proper optical path length may not be obtained, causing the image to be out of focus.
To prevent the image from being out of focus, there is proposed an optical system adjusting apparatus for adjusting the positional relationship between the first and second moving frames at the home positions thereof. Examples of such optical system adjusting apparatus include apparatus of the type of adjusting the wire end mounting positions and apparatus of the pulley wrapping type.
In the apparatus of the type of adjusting the wire end mounting positions, as disclosed by Japanese Unexamined Patent Publication No. 59-146045, a pair of wires which respectively engage with the ends of the moving frames, have fixed ends attached to the wall surface of the electrophotographic copying apparatus such that the positions of these fixed ends may be adjusted. By adjusting these positions, the moving frames may be adjusted in position.
In the apparatus of the pulley wrapping type, as disclosed by Japanese Unexamined Patent Publication No. 62-240948, a pair of wires are respectively wound several times, at the mid-portions thereof, on a pair of take-up pulleys which are secured to the prime shaft in a manner rotatable with respect thereto. By loosening the take-up pulleys with respect to the prime shaft to rotatingly adjust the pulleys in the circumferential direction, the moving frames may be adjusted in position.
In the conventional apparatus of both types, the adjustment in distance between the moving frames is achieved by alternately adjusting the distances between both ends of the respective moving frames. This disadvantageously requires much labor.